There is present in coal, especially the lower rank coals, a relatively high oxygen content, present in all probability as ether linkages bonding the cyclic structures. Carbonization of the coal, at low or high temperatures, ruptures these linkages and reforms the fragments to produce the different tar-acid molecules found in the resulting low- and high-temperature tars. Also produced during this reforming process are oxygen-containing heterocyclic ethers, such as benzofuran, more commonly known as coumarone. High temperature carbonization of bituminous coal, as practiced for production of metallurgical coke, produces coumarone which is recovered in the light-oil fractions from the coke-oven gas and the condensed tar. The work-up of the light-oil fractions to recover monocyclic aromatics such as benzene, toluene and xylene, results in isolation of an intermediate distillate product having a boiling point in the range of about 160.degree. to 200.degree. C., which is commonly referred to as the solvent naphtha fraction. A typical analysis of this fraction is given in Table I.
Table I ______________________________________ Analysis of Solvent Naphtha Fraction Component Percent.sup.1) ______________________________________ Unidentified (prob. aliphatics) 3.2 m, p-Ethyltoluene 1.2 1,3,5-Trimethylbenzene & o-ethyltoluene 5.1 1,2,4-Trimethylbenzene 11.0 .alpha.-Methylstyrene & 1,3-dimethyl-5-ethylbenzene 0.8 1,2,3-Trimethylbenzene & m,p-vinyltoluene 7.1 Indane 1.5 Unidentified 0.5 Indene 58.7 Coumarone.sup.2) 8.6 Benzonitrile 2.2 Unidentified 0.2 Tar Acids (nonaqueous titration), milliequivalents per 100 grams 1.0 ______________________________________ .sup.1) By gas-chromatographic analysis. .sup.2) Contains small proportion of methylcoumarones.
This fraction, rich in indene, a polymerizable compound, was in the past marketed for its resin-formers content. Coumarone-indene copolymer produced from the solvent naphtha fraction is a low-cost resin that once found extensive use in the manufacture of coatings and floor-coverings. However, the development of improved synthetic materials such as polyvinyl chloride has resulted in displacement of the coumarone-indene resins from these applications. Because of the large concentration of polyalkylbenzenes, as well as indene, in the solvent naphtha fraction, it was believed that an effective hydrocarbon solvent could be prepared by hydrogenation of the fraction. However, prior to the ring hydrogenation, it is first necessary to destroy the heterocyclic contaminants that otherwise would poison and inactivate conventional hydrogenation catalysts. This destruction is generally achieved by a hydrorefining reaction in which the feed is subjected to a hydrogenating atmosphere at elevated temperature and pressure and with a special refining catalyst that is capable of promoting the desired elimination reactions.
The major heterocyclic contaminant in solvent naphtha is coumarone (benzofuran). Under conventional hydrorefining conditions the following reaction would be expected to occur: ##STR1## Thus, Shuikin, et al, Chem. Abstr., 33: 1316.sup.1,2) (1939), and Shuikin et al, Chem. Abstr., 35: 2508.sup.5 (1941), examining the hydrogenation of pure furan, alkylfuran and benzofuran, found that the furans were converted to their corresponding tetrahydro derivatives when passed with hydrogen over a nickel aluminum catalyst (27% Ni - 73% Al) at 120.degree. to 140.degree. C. ##STR2## Using benzofuran and the same catalyst, the product formed was purported to consist of a mixture of 2-ethylcyclohexanol and .beta. -cyclohexylethyl alcohol. ##STR3## It is seen that hydrogenolysis under these conditions yields an alcohol resulting from saturation hydrogenation of the aromatic ring or a .beta.-substituted alcohol resulting from cleavage between the O-atom and the ring.